Node.js base64 encode a downloaded image for use in data URI

Question

Using Node v0.2.0 I am trying to fetch an image from a server, convert it into a base64 string and then embed it on the page in an image tag. I have the following code:

var express = require('express'),
request = require('request'),
sys = require('sys');

var app = express.createServer(
    express.logger(),
    express.bodyDecoder()
);

app.get('/', function(req, res){

    if(req.param("url")) {
        var url = unescape(req.param("url"));
        request({uri:url}, function (error, response, body) {
          if (!error && response.statusCode == 200) {

                var data_uri_prefix = "data:" + response.headers["content-type"] + ";base64,";
                var buf = new Buffer(body);
                var image = buf.toString('base64');

                image = data_uri_prefix + image;

                res.send('<img src="'+image+'"/>');

          }
        });
    }
});

app.listen(3000);

Note: This code requires "express" and "request". And of course, node. If you have npm installed, it should be as simple as "npm install express" or "npm install request".

Unfortunately, this doesn't work as expected. If I do the conversion with the Google logo, then I get the following at the beginning of the string:

77+9UE5HDQoaCgAAAA1JSERSAAABEwAAAF8IAwAAAO+/ve+/ve+/vSkAAAMAUExURQBzCw5xGiNmK0t+U++/vQUf77+9BiHvv70WKO+/vQkk77+9D

However if I use an online Base64 encoder with the same image, then it works perfectly. The string starts like this:

iVBORw0KGgoAAAANSUhEUgAAARMAAABfCAMAAAD8mtMpAAADAFBMVEUAcwsOcRojZitLflOWBR+aBiGQFiipCSS8DCm1Cya1FiyNKzexKTjDDSrLDS

Where am I going wrong that this isn't working correctly? I have tried so many different js base64 implementations and they all don't work in the same way. The only thing I can think of is that I am trying to convert the wrong thing into base64, but what should I convert if that is the case?

Answer 1

The problem is encoding and storing binary data in javascript strings. There's a pretty good section on this under Buffers at http://nodejs.org/api.html.

Unfortunately, the easiest way to fix this involved changing the request npm. I had to add response.setEncoding('binary'); on line 66 just below var buffer; in /path/to/lib/node/.npm/request/active/package/lib/main.js. This will work fine for this request but not others. You might want to hack it so that this is only set based on some other passed option.

I then changed var buf = new Buffer(body) to var buf = new Buffer(body, 'binary');. After this, everything worked fine.

Another way to do this, if you really didn't want to touch the request npm, would be to pass in an object that implements Writable Stream in the responseBodyStream argument to request. This object would then store the streamed data from the response in it's own buffer. Maybe there is a library that does this already... i'm not sure.

I'm going to leave it here for now, but feel free to comment if you want me to clarify anything.

EDIT

Check out comments. New solution at http://gist.github.com/583836